Signed-off-by: Mans Rullgard <mans@mansr.com>

instead of unconditionally at the start of the function.

This fixes a bug where a successful call to ff_thread_init() masks errors that
occur after that point in the function.  It also makes future bugs like this
less likely since the error code is now set near to the point in the code
where the error is found.

Fixes make install after 3453a231.

The problem with url_exist() is that it tries to open a resource in
RDONLY mode. If the file is a FIFO and there is already a reading
client, the open() call will hang.

By using avio_check() with access mode of 0, the second reading
process will check if the file exists without attempting to open it,
thus avoiding the lock.

Fix issue #1663.
Signed-off-by: Anton Khirnov <anton@khirnov.net>

Make AVIO_FLAG_ access constants work as flags, and in particular fix
the behavior of functions (such as avio_check()) which expect them to
be flags rather than modes.

This breaks API.

this should've been written earlier, sorry
Signed-off-by: Anton Khirnov <anton@khirnov.net>

This fixes a lot of warnings of the sort:
libavcodec/pcm.c:105: warning: cast discards qualifiers from pointer target type